Contact between glycerol and acetic acid in reactivedistillation column occurs along the column that will be affected by the height of packing. The higher packing materials cause contact between the two reactants better than before. The effect of higher packing materials on the glycerol conversion is shown in Fig. 7. Effect of higher packing materials resulted in an increase concentration of triacetin as product. Triacetin conversion will increase by 0.0077% at 19.5 cm interval of stuffing materials. Maximum conversion of glycerol in the process is 97.49663%.
The UNIQUAC model was selected as the property method to perform the simulation as it was also suggested by Bhatia et al. , Banchero et al. , and Lazzus . Beside the Radfrac model and UNIQUAC property method, other process equipment models such as DSTWU column, heater, mixer and heat exchanger were also considered for estimating the most suitable system configuration. Reaction kinetics constants from Table 1 were used to proceed the Radfrac simulation of reactive stages. Vacuum operating pressure was preferred to start the simulation in the purpose of finding the best-operating conditions since the boiling point of the involving components were very high. Several key parameters were first determined to run basic reactivedistillation simulation. The parameters were shown in Table 2.
The esterification of acetic acid with isopropanol is considered inside a RD column. The column has a total condenser and reboiler. The theoretical stages are numbered from top to bottom. The equations for 14 stages for the system and four-component system were solved in MATLAB by ODE45 solver. Dynamic model of reactivedistillation column was developed assuming ideal trays and phase splitting in the decanter incorporating tray to tray mass and energy balance. A MATLAB® code was written for solving the resulting ordinary differential equations-initial value problems. The data defining the column configuration, feed composition, column holdup, etc. is given in Table I. This data corresponds to the steady state of RD Column at reflux ratio of 4.
From economic optimization based on a total annual cost (TAC) analysis, the optimal configuration of reactivedistillation column consists of 24 stages and is fed at stage 21. The minimum total annual cost (TAC) is 1,150,648.47 $/year. The effect of increasing the number of stages is to increase the capital cost of the column. But the diameter of column becomes smaller because reboiler heat input decreases, this leads to decreases heat exchanger costs and operating costs.
Aspen Plus has been used for model development & simulation of reactivedistillation of esterification process . The purpose of this simulation is to carry out dynamic simulation of system & study three different control structures i) default control structure ii) single point control structure & iii) two point control structure subjected to disturbances in feed temperature and feed flow rate. In Aspen Plus simulator RD column simulated using rigorous RADFRAC unit . The physical properties considered for simulation is UNIQUAC to estimate missing parameters in Aspen database . Design parameters used in the simulation are shown in Table 1.
KATAPAK-S (S implies Sandwich) is a structured catalyst support for use in gas–liquid reaction systems such as trickle bed reactors, bubble columns or reactivedistillation processes, in which catalyst granules can be embedded Fig. 1. It is suitable for many catalytic applications, such as esterifications, etherification, and hydrogenations reaction. KATAPAK-S is immobilized between two sheets of metal wire gauze, forming “sandwiches”. Each of these sheets is corrugated, resulting in a structure with flow channels of a defined angle and hydraulic diameter. The sandwiches are assembled with the flow channels in opposed orientation, so that the resulting unit is characterized by an open cross-flow structure pattern. The sandwich exists of 16 triangular channels, with a total of 32 cross-overs. A single triangular channel has a base of 36 mm, and a height of 18 mm. There is a 2 mm gap between the bases of adjoining triangular channels Fig.
this azeotrope is a minimum boiling azeotrope, instead of pure water one gets distillate composition close to the ternary azeotrope. The azeotrope can be either homogeneous or heterogeneous. If on condensation of the vapors, the liquid forms two phases, the azeotrope is called heterogeneous azeotrope. In the present system, the azeotrope is heterogeneous and forms two liquid phases on condensation. The aqueous phase is almost pure water and organic phase that consists of mainly BA and BuOH can be recycled back to the column through reflux. Hence, ideally in the batch RD mode if one starts with stoichiometric ratio of BuOH and AcAc in the reactor, at the end of the experiment, the system should contain only BA in the reactor, if losses of BuOH and other components with the overhead aqueous phase are negligible.Reactive Distillation is an attractive method for chemical synthesis because chemical reactions and product separation occur simultaneously in the same unit. For esterification reactions it is the most effective method of synthesis.
Polyacrylate group, is of great industrial interest due to its excellent optical and medical performance as plexiglass, optical fibers, fracture fixations and bone cement respectively. Conventionally, this polymer was synthesized using batch reactor with product purity not more than 80%. To solve this conversion problem, in this paper, we proposed an innovative Poly (methyl methacrylate) process based on dual reactivedistillation unit which allows the production of high purity polymer latex with minimal cost. This study made a fair comparison between the conventional and optimally designed process based on reactivedistillation. The process was optimized by simulating the Radfrac model in Aspen Polymer plus environment. The results clearly demonstrate that the polymer latex attained the maximum purity of more than 95% in reactivedistillation column as compared to conventional method.
Wang and Wong (2006) reported that output multiplicities occur at high isopropanol purity when all the unreacted propylene was refluxed at the top of reactivedistillation. The design was extremely sensitive to stoichiometric balance in the production of high purity isopropanol. A slight decrease in water feed resulted in large increase in reboiler feed while a slight increase in water feed resulted in significant purity decrease of isopropanol. An alternative design proposed which employ a small reflux ratio and recycle some excess propylene using a recycled feed eliminate the output multiplicity although input multiplicity remains to be found. This design results in less sensitivity to variation in stoichiometric balance.
Reactivedistillation consists of both reaction and distillation in a single column, as shown in Fig. 1, in which reactants get converted to products, which are separated out in the same column [14-17]. This process has the advantages over the conventional one such as energy efficient, solvent consumption, the capital cost (because of less number of equipment’s are required) and removal of hot spot problem by liquid evaporation . The application of reactivedistillation is constrained by operating conditions viz. temperature and pressure and difficulties in proper residence time characteristics . Reactivedistillation shows good energy savings for the systems in which the reaction is fast and the reaction temperature is suitable for separation . Tavan and Hosseini  have done a parametric study on a reactivedistillation column to break the azeotrope of the ethanol (EtOH)/water system.
Abstract—A process design study was carried out, aimed at the design of a triacetin production process from glycerol, as a way to increase the feasibility of biodiesel production. Glycerol esterification with acetic acid involves three consecutive reversible acetylation reactions and in each step, water is produced, resulting in limited conversion and low selectivity . One way to increase the triacetin selectivity is to continuously remove water from the reaction medium, in order to shift the equilibrium. The proposed process is based on the reaction system described by Galan et al. , consisting of the esterification of glycerol using excess acetic acid as catalyst. In the first step of the present study an evaluation of the kinetic parameters was carried out, based on published experimental data . The reaction conditions were then evaluated in terms of glycerol conversion and selectivity for different reaction times and temperatures. Based on the results, the process was simulated in a reactivedistillation column, and different configurations were studied by using the Aspen Plus® simulator. In the separation units the NRTL-HOC equilibrium model with binary interaction parameters proposed by Hung et al.  was adopted. Water removal from the top stream of the column was increased by feeding hexane as an entrainer in the reactivedistillation column. Hexane is recovered in a separate unit and recycled to the process. The conceptual process specifications of an optimized industrial plant configuration were estimated for minimum specific energy consumption for production of 99.9 % molar purity triacetin with complete glycerol conversion.
The monothetic, also known as one-factor-at-a-time, analysis of a reactivedistillation process involving octene metathesis to produce heptene and nonene has been carried out in this work. ChemCAD, which is a process simulator, was employed to develop the model of the process while the equilibrium constant of the metathesis reaction occurring in the reaction section of the column was estimated with the aid of Aspen HYSYS via an equilibrium reactor modelling. The input variables considered as the operating factors of the process were reflux ratio, which was varied from 2 to 9, and reboiler duty, which was increased from 0.2 to 0.5 kJ/s with a step increment of 0.1 kJ/s, while the output variables were the mole fractions of heptene and nonene obtained from the top and the bottom sections of the column, respectively. The results obtained from the simulations carried out for the analysis showed that the metathesis reactivedistillation process was affected by both the reflux ratio and the reboiler duty of the column. Also discovered from the simulations was that the increase in the reflux ratio made the mole fraction of heptene obtained from the top section of the column to approach one while that of the nonene product given from the bottom section of the column was decreasing. Moreover, it was discovered that increase in the reboiler duty could make the mole fraction of the nonene collected from the bottom section of the column to approach one whereas that of the top heptene was observed to be decreasing. Therefore, it has been revealed from the monothetic analysis of the metathesis reactivedistillation process carried out in this study that the quality of the products obtained from the top and the bottom sections of the reactivedistillation column were functions of the reflux ratio and the reboiler duty.
Total operating cost includes the operating parameters like flow rate, reboiler duty, reflux ratio etc. needed to produce a product. Here we have taken reflux ratio as the basis for evaluation of optimized total operating cost. Total capital cost includes onetime investment such as land, building, equipment etc. Total number of plates in the reactivedistillation column is a crucial parameter which is to be optimized as this directly affects the reflux ratio which is again a contributing factor for the operating cost. Thus the challenge of this paper is to find the optimized value of design variables to get highest product purity with an optimized cost. Thus optimization of overall cost which includes total operating cost, total capital cost and total utility cost of reactivedistillation column is carried using economic analysis tool in Aspen plus.
Eastman Kodak has developed a reactive distilla- tion process for the manufacture of high purity and ultrahigh purity methyl acetate. The remarkable fac- tor is that, in spite of the reaction having unfavour- able equilibrium limitation, high purity product is obtained using a near-stoichiometric mole ratio of methanol and acetic acid. The reactivedistillation column used in the process is shown in Figure 4. In order to explain the process, the column can be divided in four stages starting from the top as: (1) methyl acetate enrichment; (2) water extraction; (3) reaction; and (4) methanol stripping. The reaction occurs in the middle section (section 3) in a series of countercurrent S ashing stages with sulfuric acid as the catalyst. In section 2, acetic acid acts as an ex- tracting agent and extracts water (breaking the methyl acetate } water azeotrope) and some methanol. Acetic acid and methyl acetate are separated above the acetic acid feed, in the methyl acetate-enriching section (section 1), allowing pure methyl acetate to be recovered as the overhead product. Methanol is strip- ped from water in the bottom section (section 4) and water is the bottom product. Some intermediate boiling compounds are formed because of the impu- rities present in feed. Hence, a small stream is with- drawn just above the catalyst feed point and treated separately in an impurity-removal system. The impu- rities are stripped and concentrated, and the meth- anol # methyl acetate stream is recycled to the reaction zone. The reactivedistillation column has been successfully operated at a near-stoichiometric mole ratio of acetic acid and methanol, yielding high
W ajge et al. (1997) exam ined th e accuracy and speed of num erical m ethods for sim ulating b o th reactive b atch distillation and non-reactivedistillation in packed colum ns. They in dicated th a t packed columns models differ from tra y m odel colum ns in th a t m ass transfer effects need to be considered. T hey considered th e finite difference technique which in volves converting th e differential equations to algebraic equations of sm all intervals. This m eth o d was used for th e sim ulation of batch distillation and it was concluded th a t th e finite difference m ethod is very com putationally expensive. T hey considered an orthogonal collocation m ethod where th e equations are approxim ated to polynom ials. T hey concluded th a t this was m ore efficient but the co m putational advantages over finite elem ent m ethods were lost as the need for g reater accuracy required th e use of higher order polynom ials. T hey proposed a hybrid m ethod called collocation on finite elem ents which perm its high accuracy while retaining th e use of low order polynom ials and th e ir sh o rter solution tim es. T hey also identified th a t com putation also took longer if th e com position profiles becam e widely sep arated in th e column. T hey indicated th a t th e use of sparse m a trix techniques in th e solution also yielded im proved solution tim es.
however, it was found not to be affected by loop interactions. Wang and Wong (2006) used steady state and dynamic simulations to investigate the process characteristics and control strategy of a reactivedistillation column for isopropanol (IPA) synthesis by direct hydration of propylene with the aid of PI controllers. They found a robust nominal operation of the process by maintaining an excess of propylene feed to the column and recycling the unreacted propylene to the feed instead of the top stage. Stage temperature and propylene composition with one-to-one relationship with reboiler duty and propylene feed were respectively selected as the controlled variables for maintaining bottom purity and feed ratio in the presence of possible measurement bias. High nonlinearity between the selected input–output pair was reduced by using variable transformation. Dynamic simulations demonstrated that such a control scheme with nonlinear transformed variable was capable of providing much superior control performance than the one using natural variable.
the catalyst namely heterogeneous and homogenous catalyst which can be used in reactivedistillation column. homogenous catalyst is possible in most cases of RDC but needs separation steps to recycle the catalyst. This can be avoided in heterogeneous catalyst but here special constructions are necessary to fix catalyst in reactive zone. In this column the catalytic zone consist of sulzer packing and the rectifying and stripping section consist of hyflux packing .
 G. B. Shinde, V. S. Sapkal, R. S. Sapkal, and N. B. Raut, Transesterification by reactivedistillation for synthesis and characterization of biodiesel, Biodiesel-Feedstocks and Processing Technologies, Dr. Margarita Stoytcheva (Ed.), (ISBN:978-953-307-713-0 In Tech, 2011). 289-316. Available from: http://www.intechopen.com.